Quick Answer
The answer is per-prefix label mode. This MPLS label allocation mode is correct because it assigns a single, consistent label to a specific prefix across all core routers, regardless of which router originated the route, ensuring uniform label allocation for proper forwarding and simplified troubleshooting. On the Cisco SPCOR 350-501 exam, this concept tests your understanding of how MPLS label distribution differs between modes—a common trap is confusing per-prefix with per-next-hop, which would assign different labels for the same prefix based on the next-hop router, breaking the requirement for consistency. Remember that per-prefix mode prioritizes the prefix itself over the next hop, making it ideal for scenarios where label uniformity is critical. A helpful memory tip: think "prefix first, not path"—the label sticks to the route, not the router that advertised it.
This 350-501 practice question tests your understanding of mpls and segment routing. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An engineer is deploying MPLS in the core and wants to ensure that all core routers use the same label for a specific prefix, regardless of which router originated it. Which MPLS label allocation mode should be used?
Per-interface label mode
Why wrong: Per-interface assigns a different label for each interface, not consistent across routers.
Per-next-hop label mode
Why wrong: Per-next-hop assigns labels based on next hop, not per prefix.
Per-prefix label mode
Per-prefix allocates one label per prefix, ensuring same label across all routers.
Per-VRF label mode
Why wrong: Per-VRF is for VPNs, not for core prefix labels.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Per-prefix label mode
Per-prefix label mode (option C) is correct because it assigns a single label for a specific prefix across all core routers, regardless of which router originated the route. This ensures label consistency, which is critical for proper MPLS forwarding and troubleshooting. In contrast, per-next-hop or per-interface modes would create different labels for the same prefix based on the next hop or interface, breaking the requirement for uniform label allocation.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Per-interface label mode
Why it's wrong here
Per-interface assigns a different label for each interface, not consistent across routers.
Per-next-hop label mode
Why it's wrong here
Per-next-hop assigns labels based on next hop, not per prefix.
Per-prefix label mode
Why this is correct
Per-prefix allocates one label per prefix, ensuring same label across all routers.
Related concept
Read the scenario before looking for a memorised answer.
Per-VRF label mode
Why it's wrong here
Per-VRF is for VPNs, not for core prefix labels.
Common exam traps
Cisco often tests the distinction between per-prefix and per-next-hop label modes, and the trap here is that candidates confuse per-next-hop (which creates multiple labels for the same prefix) with per-prefix, thinking that per-next-hop ensures consistency when it actually does the opposite.
Detailed technical explanation
In MPLS, per-prefix label mode is the default on most Cisco IOS platforms and is configured with the 'label mode per-prefix' command under the LDP or label-switching configuration. This mode uses a single label for each prefix in the routing table, which is advertised via LDP to all LSRs, ensuring label consistency. A real-world scenario where this matters is in MPLS TE or fast-reroute designs, where inconsistent labels could cause label-switched path (LSP) failures or misrouting.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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MPLS and Segment Routing — study guide chapter
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MPLS and Segment Routing practice questions
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FAQ
MPLS and Segment Routing — This question tests MPLS and Segment Routing — Read the scenario before looking for a memorised answer..
The correct answer is: Per-prefix label mode — Per-prefix label mode (option C) is correct because it assigns a single label for a specific prefix across all core routers, regardless of which router originated the route. This ensures label consistency, which is critical for proper MPLS forwarding and troubleshooting. In contrast, per-next-hop or per-interface modes would create different labels for the same prefix based on the next hop or interface, breaking the requirement for uniform label allocation.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.
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